GB2412929A

GB2412929A - Glass tiles

Info

Publication number: GB2412929A
Application number: GB0506739A
Authority: GB
Inventors: Isabelle Pires; Emmanuel Desesquelles; Isabelle Bernheim
Original assignee: Saint Gobain Glass France SAS; Compagnie de Saint Gobain SA
Current assignee: Saint Gobain Glass France SAS; Compagnie de Saint Gobain SA
Priority date: 2004-04-07
Filing date: 2005-04-04
Publication date: 2005-10-12
Anticipated expiration: 2025-04-04
Also published as: GB2412929B; KR101271695B1; AT503237B1; CH704036B1; CZ307357B6; PT103255B; KR20060045547A; PL374167A1; DE202005005170U1; DK177104B1; FR2868799A1; DE102005014945A1; GB0506739D0; ITMI20050559A1; DK200500481A; ES2264376B2; AT503237A2; BE1016582A3; NL1028710C2; PT103255A

Abstract

A glass wall covering comprises a glass substrate 1 coated on a mounting face with a lacquer layer 2. The lacquer layer 2 has a water permeability which enables the tile to be adhered to a mounting surface using standard adhesive mortars or bonding cements made up of sand, cement and mixing water. The lacquer layer 2 may include a synthetic resin as a binder. The synthetic resin may be based on a polyurethane resin or on a alkyd resin. An adhesion promoter, which may be based on silanes, may be provided in the lacquer or in a layer between the glass 1 and the lacquer 3. The lacquer layer may include pigments resistant to ultraviolet radiation. The glass substrate 1 may be a monolithic sheet of glass or may be a multiple glazing unit. The glass substrate 1 may have a frosted face, a reflective layer formed between the glass 1 and the lacquer 2 or may have raised features on one face. The glass wall covering may include a decoration formed by screen printing or by inkjet printing.

Description

24 1 2929

GLASS WALL COVERING

The present invention relates to a glass wall covering, especially in the form of tiles, intended to cover the surfaces of a dwelling, such as the walls, the floors or the ceilings.

The invention relates more precisely to a covering that can be fixed to the walls using standard techniques for applying conventional ceramic tiles.

Glass wall coverings, in the form of panels or tiles, are particularly appreciated for their aesthetic qualities and for their ease of maintenance. The complete absence of porosity of the glass gives it high cleanability, whereas the light transmission and reflection properties of the glass produce very prized optical effects, for example depth effects when decorations are placed on the rear face of the panels.

However, their development on a commercial scale has been handicapped, for a number of years, by the fact that the glass coverings cannot be applied to the walls by means of the cements normally used by tilers for laying ceramic tiles, such as bonding cements, also called "adhesive mortars". These are cement/sand mixtures to which water called mixing water is added so as to form a paste that can be applied to the walls to be covered and which then solidifies owing to the hydration reactions of the cement. However, cement is incompatible with standard glasses, such as glasses of a soda-lime-silica composition, as its basic nature causes glass corrosion reactions that prevent any adhesion of the glass to the cement and greatly detract from the aesthetics of the glass panel.

Various alternative means of fixing glass coverings have therefore been employed. They may be mechanical, but then require the production of expensive metal parts (screws, rivets, bolts). Mechanical assemblies, which are discontinuous, also have the drawback of producing internal stress concentrations and irregular distribution of the strength, these being prejudicial to good mechanical resistance of the assembly. They are also visible, which may detract from the aesthetic aspect.

The glass coverings may also be fixed by means of adhesives, for example those based on synthetic resins.

Owing to the high cost of the adhesives employed, these are rarely applied over the entire surface to be bonded, hence poor distribution of the shear stresses, and therefore bonding of lower quality. Furthermore, ageing reactions may be expected, which will degrade their adhesive properties.

Solutions allowing the use of bonding cements have recently been proposed, but they are not without drawbacks.

Thus, US patent No. 6 015 622 recommends the use of a very particular laying method, which includes in particular the mixing of the mortar with an aqueous dispersion of a polyacrylic acid derivative.

DE 100 34 981 claims a glass tile already coated with a cement of particular composition, obtained using an aqueous dispersion of a styrene-butadiene type resin. EP- A-722 027 also discloses the use of a specific mortar, comprising 50% of an adjuvant consisting of a dilute aqueous dispersion of a synthetic resin. In these three cases, it is essential to use a mortar of special composition, the use of mortars commonly employed by ceramic tilers not being satisfactory.

It also seems that the smooth surface of the glass is prejudicial to good fixing of the glass tile to masonry walls. FR 599 239 therefore recommended in 1925 that the tiles be coated with a layer of paste or varnish derived from synthetic resins, to which layer fragments of glass, metal, sand, gravel, marble or any other inert material are fixed. However, this method requires the use of ground fragments, coming therefore from an expensive process.

Glass wall coverings are also known from the prior art to which a layer of lacquer with a decorative function is applied to the face in contact with the wall to be covered. However, the type of lacquer employed is also incompatible with bonding cements, and such products have to be applied to the walls by other means, for example using adhesive resins.

The present invention aims to remedy the aforementioned drawbacks by proposing a glass-based wall covering, especially in the form of tiles, intended to cover the surfaces of a dwelling and being able to be applied to the said surfaces by the techniques conventionally employed for laying ceramic tiles, especially using standard bonding cements.

The inventors have discovered that the key physico- chemical characteristic in this case is the water permeability of the lacquer. When this parameter is unsuitable (in this case too high, owing to the adhesive mortar employed), the mixing water, rendered basic by the cement hydration reaction, diffuses through the lacquer layer and chemically reacts with the surface of the glass, thus rendering any adhesion (especially glass/lacquer adhesion) impossible, while degrading the appearance of the glass covering.

In its widest application, the covering according to the invention therefore comprises a glass substrate coated on the face to be applied with a lacquer-based layer, wherein the lacquer has a water permeability such that the said covering can be applied to the surfaces using standard adhesive mortars or bonding cements.

The maximum permeability of the lacquer in order for the bonding to be able to last obviously depends on the type of adhesive mortar employed. The lacquer of the covering may have a water permeability at 25 C, expressed in cm3.cm.cm2.sl.Pal, of preferably less than 10-6, or even less than 5x10-7 and especially less than 10-7. To ensure perfect adhesion and mechanical strength, especially shear strength, over long periods, it is even preferable for the lacquer to have a water permeability at 25 C of less than 10-8, or less than 10-9 and even less than 10-l cm3.cm.cm-2.sl.Pa-l. Since the present coverings are in certain cases intended to be laid in wet environments (for example in bathrooms), it is even preferable for the water permeability of the lacquer coating one face of the covering to be less than 10-ll, or less than 10-12 and even less than 10-13 cm3.cm.cm2.sl.Pal.

The water permeability is defined as the amount of water vapour diffusing through a material (in cm3) multiplied by the thickness of the material (in cm) relative to the exposed area (in cm2) multiplied by the exposure time (in seconds) and by the pressure difference (in pascals) between the two faces of the material. It can be measured, for example, by measuring the weight uptake of a lacquer film after exposure in an environmental chamber, the relative humidity of which is controlled.

In the case of a polymer, this parameter depends primarily on the chemical nature of the polymer, and then on its morphology, which for example depends on the degree of crosslinking (via, for example, the amount of crosslinking agent and/or the crosslinking temperature), on the degree of crystallization and on any orientation of the molecules. It possibly also depends on the nature and the quantity of mineral fillers.

The present lacquer for the covering therefore preferably includes a synthetic resin as binder, this preferably being in liquid form before deposition and suitable for oven drying. It has been observed that lacquers comprising binders dried at high temperature (above 50 C, or even above 100 C) quite generally have a lower permeability than binders dried in air at room temperature, probably owing to crosslinking reactions, for example polycondensation reactions, taken further towards completion and giving rise to three-dimensional networks of higher density.

Advantageously, the binder is a polyurethane resin, obtained by crosslinking, via an isocyanate or a polyisocyanate, of hydroxylated resins, especially polyester or polyether resins, or preferably acrylic resins (or polyacrylates), which have a high ultraviolet radiation resistance. In this case, the hydroxylated acrylic resin preferably derives from the polymerization of a styrene acrylic, whereas the isocyanate (or polyisocyanate) advantageously contains no aromatic-type group. This particular combination makes it possible in particular to obtain low permeabilities, good mechanical properties (for example in terms of scratch resistance) and high ultraviolet radiation resistance.

The binder for the lacquer of the covering according to the invention may also contain or be based on one or more alkyd resins obtained by chemical reaction between at least one polyol, at least one polyacid and at least one fatty acid or an oil. These alkyds are preferably short in oil, that is to say the weight content of oil or fatty acid in the resin is preferably less than or equal to 40%. The polyols may for example be glycerol or pentaerithritol compounds. The polyacids may be based on phthalic anhydride. The oils may be drying oils (such as linseed oil, wood oil or china wood oil), semi-drying oils (such as soybean oil, tall oil, safflower oil or dehydrated castor oil) or even non-drying oils (such as copra oil or castor oil). To improve their water resistance properties, the alkyd binders may also be modified by monomers such as styrene, vinyltoluene or acrylates, or by phenolic or epoxy resins. Aminoplast alkyd resins crosslinking under the effect of heat are particularly advantageous binders for the present lacquer of the covering. The aminoplast crosslinking agent is preferably a urea-formaldehyde or melamine-formaldehyde resin, which give good water resistance, especially when they are applied in an amount of 20 to 30% by weight relative to the dry alkyd binder.

The lacquer may also include a binder based on a thermosetting acrylic resin, for example obtained by the crosslinking of a carboxylated acrylic resin via an epoxy, phenol-formaldehyde or melamine-formaldehyde resin, of an acrylic resin with a carboxamide functional group via an epoxy or alkyd binder, or else of an acrylic resin with an epoxy functional group via acids or polyamines.

The present covering is advantageously provided with an adhesion promoting layer (also called an "adhesion primer") located between the glass and the lacquer, the function of which is to improve the adhesion between the glass and the lacquer. This layer is preferably based on silanes, which avoid the risk of any debonding due to moisture. Agents promoting adhesion to the glass, such as silanes, may also be dispersed in the lacquer.

Advantageously, the lacquer includes mineral and/or organic pigments, preferably mineral pigments, so as to give the desired aesthetic properties. These pigments are preferably of the type that are resistance to ultraviolet radiation and to moisture. Among the pigments employed within the context of the present invention are, for example, titanium or zirconium oxides optionally doped by ions of transition elements or else mixed oxides of the zirconium silicate (ZrSiO4) type. Preferably, the pigments are free of heavy metals, such as cadmium or lead.

The lacquer may also contain mineral fillers intended to optimise its physico-chemical parameters, for example its viscosity. The total content of mineral species (pigments and fillers) of the lacquer is preferably, expressed as a percentage by weight, between 40 and 70i, or between 50 and 60.

The present lacquer for the covering may be deposited using any type of process known to those skilled in the art, such as curtain coating, air spraying, screen printing or roll coating. The screen printing process has the advantage of being able to coat only part of the substrate. The roll coating process consists in making the substrate to be coated pass between two rolls, one of which (in general the upper roll) is coated with lacquer. For cost reasons, the process employed is preferably curtain coating, in which a flow of lacquer is created along a line approximately perpendicular to the run direction of the glass substrates, thus making it possible to coat the entire surface of the said substrates. The lacquer flow rate and the run speed of the substrate are regulated so as to deposit the desired thickness, preferably 100 to microns, in the wet state. The lacquer-coated substrate is then subjected to a heat treatment for curing the latter, more precisely for removing the solvent and for carrying out the polymerization and/or crosslinking reactions of the resins employed as binder.

Preferably, the temperature employed is between 50 and 250 C, especially between 100 and 200 C, so as to give the lacquer a degree of crosslinking suitable for reducing its water permeability. The thickness of the lacquer layer after curing is preferably between 20 and microns, especially between 40 and 70 microns, so as to obtain the desired opacity.

The glass substrate employed may be of any flat glass type (or possibly curved using bending methods known to those skilled in the art, when curved surfaces have to be covered). It may be made of monolithic glass, that is to say composed of a single sheet of glass, which may be produced by the float process for obtaining a perfectly flat and smooth sheet, or by drawing or rolling processes. In the latter case, and when the rolls of the rolling machine are embossed, the glass sheet may be impressed and have features (for example as taught in EP 493 202) on at least one of its faces, preferably the face that supports the lacquer (or rear face).

The glass may be clear or have various tints, such as blue, bronze, green, grey or even pink. The light transmission of the glass may be chosen to be between 10 and 92% for a thickness of 4 mm. One particularly preferred embodiment in the case in which the lacquer is white or ivory in colour consists in using, as glass substrate, a sheet of extra-clear glass, that is to say whose iron oxide content is less than 250 ppm, preferably less than or equal to 200 ppm or even less than 150 ppm, and the light transmission of which, under illuminant D65, is greater than 89%, especially 90%, for a thickness of 4 mm. It has been found that the optical properties of such a glass make it possible to obtain an excellent condition of the white or ivory colour of the lacquer, whereas the residual green tint of standard clear glasses, the iron oxide content of which is of the order of 1000 ppm, is particularly obvious.

The thickness of the glass substrate is preferably between 2 and 19 mm, preferably between 4 and 10 mm, and more particularly between 5 and 9 mm.

This glass sheet may be frosted on at least one of the faces (preferably the front face) by various frosting processes, for example etching with hydrofluoric acid or sandblasting. This frosting may be carried out over the entire face or over particular areas, thus creating slightly sunk frosted features. The latter embodiment may be obtained by protecting the areas that will not be etched by an acid-resistant covering, which will then be removed. The frosted appearance may also be obtained by depositing an organic or mineral enamel.

A reflective layer, preferably a layer of silver obtained by silvering processes known to those skilled in the art may also be interposed between the glass substrate (optionally provided with silane-type adhesion promoters) and the lacquer, the latter then fulfilling the function of a varnish protecting the silver layer from corrosion.

A decoration in one or more colours, obtained by screen-printing or inkjet techniques, is advantageously interposed between the glass substrate (optionally provided with silane-type adhesion promoters) and the lacquer, and/or on the front face. It is also possible to combine the application of a decoration on the front face with one on the rear face.

One particularly advantageous embodiment relates to a wall covering according to the invention, and therefore coated with a lacquer on the rear face, the said rear face then being incised by mechanical means (especially by grinding using grinding wheels of relatively complex profiles) so as to create, for example, lines from 1 to millimetres in width and from 0.5 to 3 millimetres in depth, in which all of the lacquer has therefore been removed. Such a decoration, preferably a silver layer obtained by conventional silvering techniques, can then be deposited on the rear face. If the incisions are produced as uniformly spaced lines along two orthogonal directions, it is thus possible to obtain, from a single glass panel applied against the wall, the visual impression of a multiplicity of tiles separated by joints, while still having the advantage of a front face constituting a smooth surface, thereby avoiding the problem of the joints becoming fouled and making cleaning considerably easier. This embodiment of the invention furthermore makes it possible to reduce the time required to lay the glass tiles, by saving on the grouting steps.

The glass substrate may also be coated with functional layers, such as antireflection multilayers, layers having a self-cleaning functionality (for example layers containing titanium oxide preferably crystallized in the anatase and/or rutile form, which also have anti- soiling, anti-bacterial, anti-fogging and anti- condensation properties), or else hydrophobic layers.

Layers imparting anti-slip properties, especially in the form of enamel, are particularly appreciated in the case of floor coverings. Antiabrasion or anti-scratch layers may also coat the substrate.

For safety reasons and for giving particular functionalities, the glass substrate may advantageously be a laminated glass consisting of an assembly of several glass panes, especially two glass sheets separated by a plastic sheet such as a polyvinyl butyral (PVB) sheet.

Electrically conductive layers, and therefore resistance heating layers, may be incorporated on one of the faces of the laminate, thereby making it possible to obtain, for example, heated floors and/or walls. The plastic sheet may also include liquid crystals capable of being

oriented through the action of an electric field,

allowing it to switch from a translucent or opaque state to a transparent state, for example possibly revealing a particular decoration located on the rear face.

The glass substrate may also be an illuminating window, for example double glazing filled with a gas, especially a rare gas such as xenon or neon, capable of generating, in an electric field, luminescent discharges, as described for example in the application WO 2004/015739 incorporated here by way of reference, or laminated or multiple glazing containing light-emitting diodes powered electrically by thin conductive films or by screen-printed bands or wires, for example based on a silver paste.

When the glass covering is in the form of tiling, the tiles are preferably in the form of rectangles, the lateral dimensions of which are multiples of 15 cm by taking into account a joint of a given dimension (for example 3 mm). It is thus possible to form tiles with dimensions of 15x15 cm2, 15x30 cm2, 15x45 cm2, 30x45 cm2, 30x30 cm2, 45x45 cm2 etc. The fact of taking a joint of given dimension into account for each of these dimensions makes it possible to combine tiles of different size on one and the same wall, while still maintaining alignment of the joints, this being particularly attractive from the aesthetic standpoint.

One advantage of the glass tile over conventional ceramic glass tiles lies specifically in the modularity of the possible sizes and the possibility of readily obtaining large panels. The final size is obtained by simply cutting large glass sheets, the area of which may exceed 10 m2, whereas the dimensions of ceramic tiles can be modified only by producing and using moulds of different sizes. It is also extremely difficult to obtain large ceramic parts, for example those with an area exceeding 1 m2.

The shape of the edges of the tiles has been particularly optimised so as to improve the application of joints and to avoid visible grouting defects. The inventors have observed that certain ways of making the edges, especially of the "rounded joint" type, make it difficult to apply the joints that uniformly cover the entire edge of the tile, the transparency of the glass furthermore making the possible grouting defects visible through the edge. The tiles therefore preferably have bevelled edges, which are optionally ground and/or polished, and are characterized in that the bevelled width is greater on the front face. Preferably, the rear face is very hardly affected by the shaping operation, so that the lacquer layer covers almost the entire surface of the tile. In particular, the width affected by the shaping operation on the rear face is advantageously less than or equal to 0.5 mm, or even less than or equal to 0.3 mm. In general, the lacquered area is preferably greater than the area of the front face after the shaping operation.

The present glass tiles are particularly simple to cut, requiring no specific tool other than the tool used for cutting ceramic tiles, especially vitrified stoneware tiles, or for cutting marble or granite. Likewise, the shaping of the edges after cutting may be carried out by means of a grindstone, using methods well known to those skilled in laying ceramic tiles.

We mention a few technical advantages over ceramic tiles: - the cutting precision is generally higher, hence greater compliance to tight dimensional tolerances; - the possibility of depositing the lacquer on large plates before they are cut into tiles makes it possible for the decorations, and especially the tint, to be better reproduced; and - the flatness is better, thus making it possible to reduce the overconsumption of adhesive mortar needed to compensate for any excess spaces between the covering and the wall.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figures 1 and 4 illustrate perspective views of various embodiments of the present coverings; Figures 2, 3 and 5 illustrate side views of various embodiments of the present coverings; and Figures 6 to 10 illustrate various types of patterns that can be produced by acid etching on the front face of the present covering.

Figure 1 shows a perspective view of a tile of square cross section. The tile comprises a sheet of monolithic clear glass 1 6 mm in thickness, the rear face of which is coated with a lacquer layer 2 to 50 microns in thickness, deposited using the curtain coating process. The front face has acid-etched features 3 in the form of rectangular parallelepipeds uniformly spaced along the two orthogonal directions of the tile.

The lacquer 2 after drying comprises the following ingredients: - a binder in the form of a polyurethane resin obtained by crosslinking, via a non-aromatic isocyanate, and hydroxylated acrylic resins obtained from the polymerization of a styrene acrylate; and - mineral substances (pigments and fillers) with a content of 55 by weight.

This lacquer is obtained by curtain coating followed by drying for a time of 5 minutes. The drying temperature is an important parameter for achieving sufficiently low water permeability. Under these particular conditions, and for a drying temperature below 180 C, the permeability is too high and, after bonding to a wall using an adhesive mortar, defects appear after a time of a few days, during drying of the mortar. In this case, the mixing water of the adhesive mortar passes through the lacquer layer. This causes two effects, mainly debonding between the glass layer and the lacquer layer, and etching of the glass surface. However, for a drying temperature above 180 C, the greater crosslinking of the binder of the lacquer results in a lower water permeability, generating no defect after bonding with the adhesive mortar.

Figure 2 shows a side view of the tile. The edges of the monolithic glass sheet 1 are shaped so as to have bevelled edges 4, by chamfering the edges 5 and 6, this step being carried out so that the area of the lacquered surface 2 is more than the area of the front face.

Figure 3 also illustrates a side view of a tile. In this embodiment, the rear face of the covering is coated with a silver layer 7 using a silvering process. The lacquer layer 2 covers this silver layer 7.

Figure 4 shows a perspective view of a tile formed by a laminated glazing unit formed by two glass sheets 4 mm in thickness joined together by a sheet of polyvinyl butyral 12 having a thickness of 0.76 mm. The front face is acid-etched and has features 10 in the form of waveless. One of the glass sheets has been cut away in the drawing so as to be able to reveal the presence of light- emitting diodes (LEDs) 11 on the surface of the polyvinyl butyral 13.

Figure 5 illustrates a side view of a wall covering according to the invention, which has an incision 12 with a width of 3 mm and a depth of 0. 5 mm, produced after lacquering by grinding. A silvering layer 7 is deposited and covers the lacquer layer 2 and the incised part 12. A second lacquer layer 2 (of another composition) has then been deposited over the entire silvered surface. From the front face, the silvered layer 7 is therefore visible only on the incision 12.

Figures 6 to 10 illustrate various patterns that are technically achievable by acid-etching treatments on the front face of the wall coverings. The dark parts represent the etched areas, which are therefore sunk relative to the light parts, which appear in relief.

Claims

CLAIMS: 1. Glass-based wall covering, especially in the form of tiles,

intended to cover the surfaces of a dwelling, such as the walls, the floors or the ceilings, comprising a glass substrate coated on the face to be applied with a lacquer layer, wherein the lacquer has a water permeability such that the said covering can be applied to the surfaces using standard adhesive mortars or bonding cements.
2. Wall covering according to Claim 1, wherein the lacquer has a water permeability at 25 C of less than 10- 6, especially less than 10-8 or even less than 10-13 cm3.cm cm-2.x-l Pa-1
3. Wall covering according to Claim 1 or 2, wherein the lacquer includes a synthetic resin as binder.
4. Wall covering according to Claim 3, wherein the binder is based on a polyurethane resin, especially obtained by the crosslinking of a hydroxylated acrylic resin via an isocyanate or a polyisocyanate.
5. Wall covering according to Claim 3, wherein the binder is based on an alkyd resin.
6. Wall covering according to any one of the preceding claims, wherein an adhesion promoter is present, either in the form of a layer interposed between the lacquer layer and the glass substrate, or dispersed in the lacquer.
7. Wall covering according to Claim 6, wherein the adhesion promoter is based on silanes.
8. Wall covering according to any one of the preceding claims, wherein a reflective layer, especially a silvering layer for mirrors, and/or a decoration obtained by screen printing or by inkjet is interposed between the lacquer layer and the glass substrate, optionally coated with an adhesion promoter layer.
9. Wall covering according to any one of the preceding claims, wherein the lacquer layer includes pigments resistant to ultraviolet radiation.
10. Wall covering according to any one of the preceding claims, wherein the lacquer layer includes mineral fillers with a content expressed as a percentage by weight, of between 40 and 70%.
11. Wall covering according to any one of the preceding claims, wherein the glass substrate is a sheet of monolithic glass.
12. Wall covering according to any one of Claims 1 to 10, wherein the glass substrate is a multiple glazing unit comprising a plurality of glass sheets.
13. Wall covering according to any one of the preceding claims, wherein the glass substrate has, on at least one of its faces, raised features obtained by rolling and/or acid frosting and/or sandblasting and/or etching.
14. Wall covering according to any one of the preceding claims, wherein the entire front face of the glass substrate is frosted by hydrofluoric acid or by sandblasting.
15. Wall covering according to any one of the preceding claims, wherein the glass substrate has, on at least one of its faces, preferably the front face, at least one functional layer giving optical properties (anti-reflection multilayers) and/or non-slip and/or surface properties (especially anti-fouling, anti- bacterial, self-cleaning, hydrophobic, anti-fogging, anti-scratch and anti-abrasion properties).
16. Wall covering according to Claim 12, wherein the glass substrate is a double glazing unit filled with a gas capable of generating glow discharges in an

electric field.
17. Wall covering according to Claim 12, wherein the glass substrate is a laminated or multiple glazing unit containing light-emitting diodes.
18. Wall covering according to any one of the preceding claims, wherein the area of the lacquered surface is greater than the area of the front face before the shaping operation.
19. Wall covering according to any one of the preceding claims, wherein part of the rear face is incised by mechanical means and then coated with a decorative layer, preferably a silver layer obtained by conventional silvering techniques.
20. Wall covering according to Claim 19, wherein the incisions are made in the form of lines from 1 to millimetres in width and from 0.5 to 3 millimetres in depth, as straight lines uniformly spaced apart along two orthogonal directions.
21. Wall covering according to any one of the preceding claims, comprising a decoration obtained by screen printing or ink jet deposited on a rear face of the glass substrate.
22. Glass-based wall covering, which includes a decoration obtained by screen printing or by inkjet deposited on the rear face of a glass substrate.
23. A wall covering, substantially as hereinbefore described with reference to the accompanying drawings.